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FLORA INDICA.                                 173
they present; and tlie mere fact of there being in some cases definite periods for the
formation a.ud suppression of the liber, indicates the existence x>f functions that will
one day find expression as natural laws. In pursuance of Decaisne's investigations,
we would recommend the study of the anatomy of the intern odes of various parts of
the stem, in relation to the development of flower-buds and leaf-buds on the parts
above them.
The absence of annual rings of growth in wood many years old, indicates a more
geueral vitality in the stem, or, at least, a less definite boundary between the living
and dead wood; in other words, a more generally diffused activity of the stem seems
neeessaiy to the life of the plant than is usual amongst Exogens, whose inner layers
of wood are virtually inactive. The very frequently woody nature of the pith-cells,
which form- long cylindrical rigid tubes with blunt square ends, placed above one
another, would also appear to be au adaptation of that part to some modification of
its usual functions; but for what special design, we have no idea.
2. The question whether the structure of Menisperms approaches that of Endogens,
has been well answered by Decaisne in the negative; but as there are still two opi-
nions on the subject, we shall view this point in another light from that excellent
author. If the Endogenous stem is regarded as an imperfect development of the
Exogenous, and if (as is perhaps the general opinion) an annual addition to a once-
formed deposit of pleurenchyma and parenchyma, etc,, be considered typical of the
highest-developed Exogenous stem, then Menisperms may, inasmuch as they depart
from these characteristics, be considered to tend towards Endogens j but if, on the
other hand, the Endogenous stem be considered as constructed upon a totally diffe-
rent ty-pe from the Exogenous, and that the terms high and low are not applicable to
them in auy but general terms, we lose sight of any transition being indicated by
Menisperms from the Exogenous to the Endogenous type; for whereas they offer
all the peculiarities of the Exogen as contradistinguished from the Eudogen, they
share none of the distinguishing characters of the latter. The mere resemblance
of a transverse seel ion of a Menispermeous stem, with several rather irregularly de-
posited zones of wood, to-aii Endogen, argues nothing, for the structure of the bundles
thus compared is totally dissimilar, no less than their relations to one another; and
whatever casual resemblance transverse sections show in these cases (and upon which
so much stress is laid), a vertical section annuls.
The fundamental facts, that the vascular system of Menisperms is double, that each
in ninny cases, and one in all, increases annually, that the wood-bundles are sepa-
rated by continuous narrow medullary rays, and that on a vertical section the wood-
zones are all seen traversing the stem in straight lines, and always parallel to one
another, arc entirely opposed to the view which would consider the Menispermeous
stem as showing an approach to that typical of Endogens.
3. The Exogenous Orders to which Menisperms may be supposed to betray an
affinity in the structure of their stems are mentioned above, but identity of structure
is hardly to be found between Menispermacea and any of them. The greatest resem-
blance exists perhaps in Myzodendron, an erect-growing Sanfalaceous plant, and the
horizontal rhizomes of some BalanQphorea> but upon these it would be superfluous
to dwell. Much stress has been laid upon the resemblance to Aristolochia, and
Decaisne has exposed the mistaken views upon which, this was founded, showing, in
the first place, that this is neither constant nor of importance; and in the second,
that the genus Anstolocliia. presents as many variations from a common type aa
. Metiispermacea do, and that these deviations are neither common to both Orders
nor analogous in each.
In the present state of our knowledge, we cannot do better than quote Decaisue's
remarks,"that "no special value can be attached to characters drawn from the organs
of nutrition," and that'" all observations tend to prove (as Mirbd has already said)
that the anatomical structure of wood offers no sure guide to affinity.'.'
We have still a few words to add upon the individual peculiarities of Menispermeous
woods, "With regard to any agreement in wood structure amongst themselves, which
the plants of this Ordcr^show, it is very vague; closely allied genera have often very